Abrasive wear/corrosion properties and TEM analysis of Al2O3 coatings fabricated using plasma electrolysis

Alumina coatings were deposited on Al alloy substrates using an electrolytic plasma technique, based on a dielectric barrier discharge created during anodic oxidation in an aqueous electrolyte. The substrate material (BS Al 6082) was biased anodically with an unbalanced AC high voltage. During processing, a plasma current density of 100 mA/cm(2) was used, at which a coating deposition rate of 1.67 mum/min was achieved. Coating abrasive wear and corrosion properties were assessed by conducting dry and wet rubber wheel abrasive tests and potentiodynamic polarization experiments, respectively. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) were used to investigate the coating microstructure, and the coating/substrate interface. The property test results show that the coatings possess excellent abrasive wear and corrosion resistance. XRD analyses indicate that the coatings consist of alpha- and gamma-Al2O3. An amorphous + nanocrystalline inner layer (1.5-mum thick) and a nanocrystalline (50-60 nm) intermediate layer in the coating were observed by TEM. The higher resistance to wear and corrosion can in part be attributed to the presence of these interlayers. (C) 2002 Elsevier Science B.V All rights reserved.